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| United States Patent |
6,214,931
|
|
Segers
, et al.
|
April 10, 2001
|
Pressure-sensitive adhesives and self-adhesive films using said adhesives
Abstract
Pressure sensitive adhesives comprised of an aqueous dispersion of a
copolymer of acrylic esters obtained in the presence of a crosslinking
monomer carrying a functional group are set forth, said copolymer having a
glass transition temperature which does not exceed 0.degree. C. The
crosslinking monomer is methacrylic anhydride. The resulting adhesive
displays improved adhesion and cohesion properties.
| Inventors:
|
Segers; Willy (Jurbise, BE);
Hoebeke; Jean-Marie (Thimeon, BE);
Loutz; Jean-Marie (Brussels, BE)
|
| Assignee:
|
UCB, S.A. (Brussels, BE)
|
| Appl. No.:
|
117215 |
| Filed:
|
April 21, 1999 |
| PCT Filed:
|
January 1, 1997
|
| PCT NO:
|
PCT/BE97/00009
|
| 371 Date:
|
April 21, 1999
|
| 102(e) Date:
|
April 21, 1999
|
| PCT PUB.NO.:
|
WO97/27261 |
| PCT PUB. Date:
|
July 31, 1997 |
Foreign Application Priority Data
| Current U.S. Class: |
525/34; 428/355AC; 525/35 |
| Intern'l Class: |
C08F 220/18; C09J 007/02 |
| Field of Search: |
522/34,35
428/355 AC
|
References Cited
U.S. Patent Documents
| 3983297 | Sep., 1976 | Ono et al. | 428/355.
|
| 3998997 | Dec., 1976 | Mowdood et al. | 526/271.
|
| 4077926 | Mar., 1978 | Sanderson et al. | 260/29.
|
| Foreign Patent Documents |
| 2-3404 | Jan., 1990 | JP.
| |
Other References
Asmussen et al., "Solubility Parameters, Fractional Polarities, and Bond
Strengths of Some Intermediary Resins Used in Dentin Bonding", Journal of
Dental Research, vol. 72, No. 3, Mar. 1993, pp. 558-565.
|
Primary Examiner: Zirker; Daniel
Attorney, Agent or Firm: Wenderoth, Lind & Ponack, L.L.P.
Claims
What is claimed is:
1. Pressure-sensitive adhesive comprising an aqueous dispersion of an
acrylic ester copolymer obtained in the presence of a crosslinking monomer
bearing a functional group, the copolymer having a glass transition
temperature which does not exceed 0.degree. C., wherein the crosslinking
monomer is methacrylic anhydride, and is used in a quantity of from 0.4 to
2.5% by weight of the solid materials in the dispersion, and wherein the
pressure-sensitive adhesive has all of the following properties:
a shear strength, measured according to FINAT method No. 8, at least equal
to 5000 minutes,
a contact aggressiveness, measured according to FINAT method No. 9, at
least equal to 7 N/25 mm, and
an adhesion to glass at 180.degree. after 20 minutes, according to FINAT
method No. 1, after 7 days of pasting at 60.degree. C., at least equal to
8 N/25 mm.
2. Pressure-sensitive adhesive according to claim 1, wherein the acrylic
esters forming part of the composition of the copolymer are acrylic and
methacrylic esters, the homopolymer of which has a glass transition
temperature not exceeding 10.degree. C.
3. Pressure-sensitive adhesive according to claim 1, wherein the esters are
selected from acrylates having from 1 to 8 carbon atoms in the ester
radical and methacrylates having at least 5 carbon atoms in the ester
radical.
4. Pressure-sensitive adhesive according to claim 1, which also comprises
at least one chain-transfer agent.
5. Pressure-sensitive adhesive according to claim 4, wherein the
chain-transfer agent is selected from thioglycolic acid, alkylthioacetic
acid, mercaptans, water-soluble saturated hydroxyaliphatic compounds,
hydroxyalkyl aliphatic amines, monohydric alcohols and carbon
tetrabromide.
6. Pressure-sensitive adhesive according to claim 5, wherein the
chain-transfer agent is present in a proportion of between 0.05 and 2% by
weight of the solid materials.
7. Pressure-sensitive adhesive according to claim 1, which also comprises
at least one unsaturated carboxylic acid in an amount of between 0.5 and
5% by weight of the solid materials.
8. Pressure-sensitive adhesive according to claim 1, wherein the aqueous
dispersion comprises from 57 to 75% by weight of acrylic copolymer and
from 43 to 25% by weight of water.
9. Pressure-sensitive adhesive according to claim 1, wherein the pH of the
aqueous dispersion is between 3.5 and 5.0.
10. Pressure-sensitive adhesive according to claim 1, wherein the average
particle size of the dispersion is between 270 and 500 nanometers.
11. Pressure-sensitive adhesive film containing, on one of its faces, a
layer of a pressure-sensitive adhesive in accordance with claim 1.
Description
The present invention relates to pressure-sensitive adhesives, i.e.
adhesives whose adhesion to a given substrate is obtained after simple
application of light pressure. More particularly, the present invention
relates to such pressure-sensitive adhesives, which are in aqueous
emulsion form and have improved remanence of the adhesive properties when
the said adhesives are applied to various substrates, in particular films
of polyvinyl chloride, polyethylene, polypropylene, polyethylene
terephthalate, paper, glass, etc. The present invention also relates to
self-adhesive films and to other similar articles using the said
adhesives.
Pressure-sensitive adhesives intended for plasticized polyvinyl chloride
were originally obtained by radical polymerization in organic solvents
such as ethyl acetate, toluene or hexane, or alternatively in a
combination of several of these solvents. In view of the nature of the
parameters governing radical copolymerization in solvents, leading to low
molecular masses, these products necessarily had to undergo considerable
post-crosslinking in order to have an equilibrium between the various
adhesive properties, which are compatible with the requirements inherent
to the very nature of plasticized polyvinyl chloride. This means, for
example, that the internal cohesion of the product must be sufficient to
be able to compensate for the adverse changes in the properties due to the
migration of the polyvinyl chloride plasticizers.
For obvious reasons of environmental protection, the pressure-sensitive
adhesives obtained as an aqueous emulsion are nowadays preferred to those
obtained in solution in an organic solvent. Thus, U.S. Pat. No. 3,983,297
discloses a pressure-sensitive adhesive comprising, as main constituent, a
copolymer prepared as an emulsion comprising (1) 94 to 98 mol % of at
least one alkyl acrylate, where appropriate as a mixture with methyl
methacrylate or vinyl acetate, (2) 2 to 6 mol % of acrylic acid and/or
methacrylic acid, and (3) 0.002 to 0.05 mol % of a copolymerizable
polyfunctional compound. Similarly, U.S. Pat. No. 3,998,997 describes a
pressure-sensitive adhesive obtained by emulsion polymerization of a
monomer system comprising (1) 50 to 60 parts by weight of 2-ethylhexyl
acrylate, (2) 35 to 45 parts by weight of ethyl acrylate, (3) 1 to 3 parts
by weight of acrylic acid, (4) 2 to 5 parts by weight of diacetophenone
acrylamide or diacetone acrylamide and, where appropriate, hydroxypropyl
(meth)acrylate, and/or maleic anhydride, and/or glycidyl (meth)acrylate
and/or a polyfunctional vinylic crosslinking agent.
Japanese patent application published under No. 2-003,404 teaches the
emulsion polymerization of a monomer mixture comprising:
(A) from 60 to 99% by weight of a (C.sub.4 -C.sub.8)alkyl acrylate,
(B) from 0.2 to 10% by weight of a functional monomer chose from
.alpha.,.beta.-unsaturated carboxylic acids and their anhydrides,
2-hydroxyalkyl (meth)acrylates and (methylol) (meth)acrylamides, and
(C) from 0 to 30% of another vinyl monomer,
in the presence of a water-soluble compound chosen from dihydrofuran,
dihydropyran and methylcyclohexenedicarboxylic and norbornenedicarboxylic
acids, in order to obtain a copolymer dispersion having a glass transition
temperature of from -10 to -90.degree. C.
In the case of the pressure-sensitive adhesives obtained in solution form,
it is possible to obtain an acceptable compromise between the adhesion and
the adhesive power (tack), on the one hand, and the cohesion, on the other
hand, by crosslinking the product using, for example, metal chelates. This
technique offers fairly wide flexibility and allows the properties of the
product to be adjusted fairly easily to the desired level.
In the case of the pressure-sensitive adhesives obtained in emulsion form,
the problem is considerably more complex since there is greater dispersity
in the molar mass distribution; furthermore, the equilibrium of the
product is also disrupted by the presence of a series of polymerization
auxiliaries such as emulsifiers, which are external to the polymer chains,
and which can behave, for example, as plasticizers. It is accepted in
particular that the presence of long acrylic chains, which are
characteristic of emulsion polymerization, is responsible for the lack of
adhesion of these products.
If the length of the acrylic chains is reduced (for example by using a
transfer agent during the emulsion polymerization), the adhesion is indeed
improved (peel strength), but, in this case, the cohesion is lost (shear
strength), since it is generally accepted that long chains are needed in
order to obtain acceptable cohesion.
Many means have been mentioned in the literature to bring the cohesion of
the pressure-sensitive adhesives obtained in emulsion form to the desired
level while at the same time maintaining aggressiveness of contact (as
defined below), at least equal to 7 N/25 mm approximately. One of the
means most commonly used is the copolymerization of functionalized
monomers such as N-methylolacrylamide. This monomer effectively makes it
possible to increase the internal cohesion of the product, but at the
expense of the other properties. Furthermore, these properties are greatly
influenced by the heat treatment to which the copolymer has been
subjected.
In addition, the presence in N-methylolacrylamide of certain impurities
such as acrylamide or formaldehyde can also produce harmful effects, such
as adverse increases in viscosity. Other means for increasing the
cohesion, such as the use of functional silanes bearing a double bond (for
example propyltrimethoxysilane methacrylate or vinyltriethoxysilane
methacrylate), give rise to problems of degradation of the properties over
time or alternatively can only be used in the context of a two-component
system, which imposes practical constraints on the user that are often
unacceptable.
Lastly, aqueous dispersions, used in particular in heat-resistant adhesive
compositions or contact adhesives, are known from patent application
EP-A-620,234, these dispersions being prepared by emulsion polymerization
of a monomer, a homopolymer of which has a glass transition temperature
(Tg) of greater than 30.degree. C. and has only one ethylenic unsaturation
in the molecule, and of a flexible monomer, a homopolymer of which has a
glass transition temperature of less than 10.degree. C. and at most has
one ethylenic unsaturation in the molecule, the proportions of the two
monomers being such that the glass transition temperature of the copolymer
is between 5 and 25.degree. C., in the presence of methacrylic anhydride
as crosslinking monomer.
These aqueous dispersions, the water content of which is from 45 to 55% by
weight, do not, however, afford pressure-sensitive adhesives which have
the desired compromise of adhesion and cohesion properties. The state of
the art can thus be summarized in the field of the pressure-sensitive
acrylic adhesives obtained in emulsion form by the fact that, on account
of the antagonistic effects exerted by long-chain acrylics on these two
properties, it is difficult to obtain a good compromise between adhesion
and cohesion in aqueous emulsion form.
The problem for the invention to solve thus consists in developing a
pressure-sensitive adhesive which can be applied in particular to
polyvinyl chloride, polyethylene, polypropylene, polyethylene
terephthalate, paper, glass, etc. and which has both a cohesion which is
sufficient to combat the effects of migration of the plasticizers, and an
initial adhesion and tack which are sufficiently high, in order to retain
an acceptable level of properties after ageing of the product. It is
generally accepted that a product has correct accelerated ageing if the
value of the adhesive properties, measured after the film has remained for
7 days in an oven at 60.degree. C., remains equal to or greater than 60%
of the values measured initially.
This problem is solved by the present invention in the context of a
pressure-sensitive adhesive one-component system consisting of an aqueous
dispersion of an acrylic ester copolymer obtained in the presence of a
crosslinking monomer bearing a functional group, the said copolymer having
a glass transition temperature which does not exceed 0.degree. C.,
characterized in that the said crosslinking monomer is methacrylic
anhydride.
The acrylic esters forming part of the composition of a copolymer as
defined above are well known in the prior art. These are, on the one hand,
acrylic and methacrylic esters, the homopolymer of which has a glass
transition temperature not exceeding 10.degree. C., such as acrylates
having from 1 to 8 carbon atoms in the ester radical and methacrylates
having at least 5 carbon atoms in the ester radical. These esters are
usually denoted in the art as forming part of flexible monomers, in
contrast with hard monomers (the homopolymer of which has a glass
transition temperature at least equal to 20.degree. C.), such as styrene,
methacrylates having not more than 4 carbon atoms in the ester radical,
and certain acrylates such as t-butyl acrylate, n-tetradecyl acrylate and
n-hexadecyl acrylate.
As examples of acrylic esters forming part of the present invention,
mention may be made in particular of methyl, ethyl, isopropyl, n-propyl,
isobutyl, n-butyl, 2-ethylhexyl and n-octyl acrylates, as well as
n-pentyl, n-hexyl, n-octyl, n-decyl, n-dodecyl, n-tetradecyl and
n-isobornyl methacrylates. Preferably, the copolymer of the aqueous
dispersion according to the invention comprises at least two flexible
acrylic esters as defined above, and the proportions of which are such
that the glass transition temperature of the copolymer does not exceed
0.degree. C. Preferably, this set of at least two flexible acrylic esters
comprises, on the one hand, a main monomer, i.e. one which is present in a
proportion of at least 50% by weight of the set, and, on the other hand,
one or more secondary monomers present in a proportion of less than 50% by
weight of the set. According to a more particularly preferred embodiment
of the present invention, the set of flexible acrylic esters comprises
from 50 to 90% by weight of 2-ethylhexyl acrylate and the remainder to
100% of acrylate(s) and/or methacrylate(s), the homopolymer(s) of which
has (have) one (or more) glass transition temperature(s) above that of
poly(2-ethylhexyl acrylate) (-70.degree. C.).
One of the essential features of the present invention consists of the fact
that the acrylic copolymer whose Tg does not exceed 0.degree. C. is
modified by crosslinking with methacrylic anhydride. Depending on the
commercial availabilities and the manufacturing constraints, the
methacrylic anhydride used for the preparation of the modified acrylic
copolymer in aqueous dispersion form is usually a product with a purity at
least equal to 96% by weight, also comprising up to 3% by weight of
methacrylic acid, as well as up to 0.2% by weight of at least one
polymerization inhibitor (usually of phenolic type, such as
butylhydroxytoluene) and the remainder to 100% of various impurities.
Another essential feature of the present invention lies in the fact that
the crosslinking monomer affords advantageous technical effects on the
properties of the pressure-sensitive adhesive already when its weight
proportion of solid materials in the dispersion is very low. Indeed,
methacrylic anhydride preferably represents between 0.4 and 2.5%
approximately, and more particularly between 0.5% and 1.5%, by weight of
solid materials in the dispersion. It is observed that proportions greater
than 2.5% by weight provide no additional improvement in the properties of
the adhesive and can lead to difficulties in synthesizing the emulsion on
account of the well known tendency of methacrylic anhydride to precipitate
in water, forming a gelatinous mass.
An additional improvement of the properties of the adhesive according to
the invention can be obtained when the aqueous dispersion also comprises
at least one chain-transfer agent. The choice of methacrylic anhydride as
crosslinking monomer has the advantage of allowing the use of very common
chain-transfer agents instead of the very specific water-soluble compounds
of JP-A-2/003,404. These chain-transfer agents generally comprise at lest
one group containing an active hydrogen, such as a hydroxyl or --SH group
as chain-transfer group. As examples of chain-transfer agents which can be
used in the aqueous dispersion according to the invention, mention may be
made of thioglycolic acid, alkylthioacetic acid, mercaptans such as butyl
mercaptan, n-dodecyl mercaptan and dodecylbenzyl mercaptan, as well as
water-soluble saturated hydroxyaliphatic compounds. Among these compounds,
mention may be made in particular, of saturated hydroxyalkyl aliphatic
amines such as tetrahydroxyethylethylenediamine, and monohydric alcohols
such as isopropanol, isobutanol, isoamyl alcohol, isohexanol and
cyclohexanol. Preferably, the chain-transfer agent is present in the
aqueous dispersion according to the invention in a proportion of between
about 0.05 and 2% by weight of the solid materials, depending on the type
of agent chosen. By way of example, a mercaptan will usually be chosen in
a proportion of between 0.05 and 0.2% approximately by weight of solid
materials, whereas a monohydric alcohol will rather be chosen in a
proportion of between 1 and 2% approximately by weight of solid materials
in the dispersion.
The unreacted chain-transfer agent can readily be detected by
headspace-injection gas chromatography.
As is well known in the art, the aqueous dispersion according to the
invention can also comprise at least one unsaturated carboxylic acid, in
an amount preferably of between 0.5 and 5% by weight, more particularly
between 2.5 and 5% by weight, of the solid materials in the dispersion. As
examples, mention may be made of .alpha.,.beta.-ethylenically unsaturated
acids such as acrylic acid, methacrylic acid, maleic acid and fumaric
acid.
The synthesis of the aqueous dispersion according to the invention is
carried out under standard emulsion polymerization conditions, using, as
catalyst, a persulphate such as ammonium persulphate, potassium
persulphate or sodium persulphate in a proportion of from 0.1 to 0.5%
approximately of the total weight of the monomers and preferably using an
activator chosen from sulphites, hydrogenosulphites and metabisulphites,
with most particular preference for sodium metabisulphite. The catalytic
system can also comprise an organic peroxide or hydroperoxide, or
alternatively a redox system. The emulsion is obtained using surfactants
which are, preferably, mixtures of at least one nonionic surfactant and at
least one anionic surfactant. As anionic agents, mention may be made in
particular of alkyl sulphates, alkyl sulphonates and alkylaryl
sulphonates, as well as esters of sulphosuccinic acid with alkanols. An
example more particularly preferred is sodium nonylphenol polyglycol ether
sulphate. As nonionic agents, mention may be made in particular of
nonylphenol ethoxylates comprising from 4 to about 100 ethylene oxide
groups in the molecule.
The polymerization is generally carried out at a temperature of between 50
and 85.degree. C. approximately, and preferably between 70 and 85.degree.
C. It can be carried out at normal pressure, but also at a pressure above
atmospheric pressure or under a slight negative pressure, without this
adversely affecting the reaction.
Depending on the subsequent uses, the aqueous dispersion constituting the
pressure-sensitive adhesive according to the invention preferably
comprises from 57 to 75% approximately by weight of acrylic copolymer and
from 43 to 25% approximately by weight of water. It can also be
characterized by the following, preferable, particular features:
a pH of between 3.5 and 5.0 approximately,
an average particle size in the dispersion of between 270 and 500
nanometers (nm) approximately.
The pressure-sensitive adhesives according to the present invention have
not only the desired compromise of satisfactory adhesion and cohesion
properties, but also, and especially, entirely noteworthy remanence of
these properties over time, including under severe temperature conditions.
This remanence is reflected in particular by properties which, when
measured after the film has stayed for 7 days in an oven at 60.degree. C.,
remain at least equal to 60%, preferably at least 90%, of the values
measured initially. The pressure-sensitive adhesives according to the
present invention are also characterized by the transparency of their
films and their absence of yellowing over time.
According to a second aspect, the present invention thus relates to a
pressure-sensitive adhesive in the form of an aqueous dispersion having
all of the following properties:
a shear strength, measured according to FINAT method No. 8, at least equal
to 5000 minutes approximately,
a contact aggressiveness, measured according to FINAT method No. 9, at
least equal to 7 N/25 mm approximately, and
an adhesion to glass at 180.degree. after 20 minutes, according to the
FINAT method No. 1, after 7 days of pasting at 60.degree. C., at least
equal to 8 N/25 mm approximately.
Preferably, such an adhesive consists of a copolymer mainly of
(meth)acrylic monomers.
The pressure-sensitive adhesives according to the present invention can
also comprise, for certain specific applications, one or more biocides
such as, in particular, chloro and non-chloro isothiazolones, in
particular 2-methyl-4-isothiazolin-3-one and
5-chloro-2-methyl-4-isothiazolin-3-one.
According to a third aspect, the present invention relates to self-adhesive
films based, in particular, on plasticized polyvinyl chloride,
polyethylene, polypropylene, polyethylene terephthalate or paper, etc.
containing, on one of their faces, a pressure-sensitive adhesive layer as
described above. Such films find various applications in fields such as
labelling, decoration and lettering.
The examples which follow illustrate the invention. Except where otherwise
mentioned, all the amounts are expressed on a weight basis.
EXAMPLE 1
The following ingredients are loaded, at room temperature and in the
following order, into a vat equipped with a suitable stirrer:
demineralized water 481.6 parts
sodium carbonate 2.8 parts
cyclohexanol 21 parts
Sermul EA 146 100.1 parts
Sermul EA 146 is an anionic emulsifier based on sodium nonylphenol
polyglycol ether sold by the company Servo Delden B.V.
The stirring is continued in this vat until the solution obtained is of
entirely uniform appearance, after which the monomers below are dispersed
in this vat:
2-ethylhexyl acrylate 980 parts
ethyl acrylate 175 parts
methyl acrylate 175 parts
methacrylic acid 42 parts
acrylic acid 14 parts
methacrylic anhydride 14 parts
Separately, 350 parts of water and 3.5 parts of a 10% solution of a
nonionic emulsifier sold under the name Synperonic NP 40/70 are
successively loaded into a jacketed reactor equipped with a condenser, a
suitable stirrer and a thermocouple, after which the contents of the
reactor are heated to 80.degree. C. When this temperature is reached, 4.2
parts of ammonium persulphate are added and then, using a metering pump,
over a period of 4 hours and while maintaining the temperature between 80
and 82.degree. C., all of the pre-emulsion of monomers from the vat is
added.
When the addition is complete, the reaction is left to continue for 1 hour,
while maintaining the bulk temperature between 80 and 82.degree. C. This
temperature is then lowered to 60.degree. C. and the following are then
added:
10% iron(III) nitrate solution 3 drops
10% Luperox H solution 7 parts
5% Rongalit C solution 14 parts
The Luperox H70 solution is added over a period of about 15 minutes,
whereas the Rongalit C solution is introduced over 30 minutes. Rongalit C
is a sodium formaldehyde sulphoxylate sold by BASF A.G. Luperox H70 is an
organic peroxide sold by Luperox GmbH.
After cooling to room temperature, the following are added:
Biocide K10 2.4 parts
5% Borchigel L75 solution 11.9 parts
The biocide K10 is a composition based on 2-methyl-4-isothiazolin-3-one
sold by the company Progiven. Where appropriate, it can be replaced in
equivalent amount by Acticide SPX, which is an aqueous 1.5% solution of a
mixture of 5-chloro-2-methyl-4-isothiazolin-3-one and
2-methyl-4-isothiazolin-3-one, sold by the company Thor Chemicals (UK)
Ltd. Borchigel L75 is a viscosity modifier which is recommended for
thickening acrylic dispersions.
A lump-free latex is thus obtained, the physical characteristics of which
are as follows:
content of solid materials 60%
Brookfield viscosity at 50 rpm 150 mPa.s
pH 4.3
The adhesive properties are evaluated in the following way:
the liquid product is coated onto a silicone paper so as to obtain a dry
deposit of about 20 g/m.sup.2. The wet film is transferred into a
ventilated oven and dried for 3 minutes at a temperature of 110.degree. C.
The final complex is obtained by applying the film of adhesive to a film
of plasticized polyvinyl chloride.
This complex then undergoes the following conditioning:
24 hours at 23.degree. C. and 50% relative humidity,
7 days at 60.degree. C.
The following adhesive characteristics are measured on this complex:
peel strength (adhesion to glass after 20 minutes and 24 hours of pasting)
contact aggressiveness ("looptack") on glass
shear strength
For the product in dispersion form described above, the characteristics
indicated in Table I below are obtained.
The characteristics of adhesion to glass at 180.degree. after 20 minutes or
24 hours of pasting were measured according to the FINAT No. 1 test method
(and expressed in N/25 mm) and the shear strength was measured according
to FINAT method No. 8 and expressed in minutes. The contact aggressiveness
("looptack") was measured according to FINAT standard No. 9 and expressed
in N/25 mm.
Example 2 (Comparative)
The procedure of Example 1 is repeated, except that the methacrylic
anhydride is replaced with an equivalent weight-amount of a conventional
crosslinking monomer, N-methylolacrylamide. The adhesion characteristics
of the dispersion product thus obtained were measured under the same
conditions as those of Example 1 and the results of these measurements are
indicated in Table I below.
Example 3
The procedure of Example 1 is repeated, except that the cyclohexanol is
replaced with an equivalent weight-amount of another transfer agent,
isopropanol. The adhesion characteristics of the dispersion product thus
obtained were measured under the same conditions as those of Example 1 and
the results of these measurements are indicated in Table I below.
Example 4
The procedure of Example 3 is repeated, except that the amount of
methacrylic anhydride is brought to 28 parts (i.e. 2% of the acrylic
monomers). The adhesion characteristics of the dispersion product thus
obtained were measured under the same conditions as in Example 1, and the
results of these measurements are indicated in Table I below.
Example 5
The procedure of Example 1 is repeated, except that the cyclohexanol is
replaced with 1.4 parts of n-dodecyl mercaptan. The adhesion
characteristics of the dispersion product thus obtained were measured
under the same conditions as those of Example 1, and the results of these
measurements are indicated in Table I below.
Example 6
The procedure of Example 3 is repeated except that the 2-ethylhexyl
acrylate is replaced by an equivalent weight-amount of butyl acrylate. The
average particle size of the dispersion obtained is 425 nanometers. Its
adhesion characteristics, measured under the same conditions as those of
Example 1, are indicated in Table I below.
TABLE I
Exam- Exam- Exam- Exam- Exam- Exam-
Property ple 1 ple 2 ple 3 ple 4 ple 5 ple 6
Adhesion 12.0 10.0 14.6 10.0 9.0 14.0
at
20 min
(23.degree. C.)
Adhesion 10.0 17.2 19.3 18.0 18.0 15.0
at 24 h
(23.degree. C.)
Adhesion 12.5 1.9 9.3 10.0 11.0 17.0
at
20 min
after
7 days
at 60.degree. C.
Shear >10,000 4600 >10,000 >10,000 >10,000 >10,000
Aggres- 14.0 14.3 14.5 9.5 9.5 7.0
siveness
pH 4.5 .sup.(1) 4.3 4.3 4.5 4.6
.sup.(1) property not determined for this example.
The results collated in Table I show that, compared with Comparative
Example 2, the present invention provides:
maintenance or improvement in the peel strength at room temperature,
very considerable improvement (multiplication by a factor at least equal to
5) of the peel strength under severe conditions (7 days at 60.degree. C.),
and
considerable improvement (multiplication by a factor at least equal to 2)
of the shear strength.
Example 7
The procedure of Example 1 is repeated, except that the amount of
demineralized water is decreased so as to adjust the content of solid
materials to 65%, and except that the cyclohexanol is replaced with an
equivalent weight-amount of another transfer agent, sec-butanol. The
physicochemical characteristics (pH, average particle size) and adhesion
characteristics of the product thus obtained, measured under the same
conditions as in Example 1, are indicated in Table II below.
Example 8
The procedure of Example 7 is repeated, except that the sec-butanol is
replaced with another transfer agent, thioglycolic acid, in a proportion
of 0.05% by weight relative to the acrylic monomers. The characteristics
of the product obtained are reported in Table II below.
Example 9
The procedure of Example 7 is repeated, except that the sec-butanol is
replaced with another transfer agent, carbon tetrabromide, in a proportion
of 0.1% by weight relative to the acrylic monomers. The characteristics of
the product obtained are reported in Table II below.
Example 10
The procedure of Example 1 is repeated, except that the transfer agent is
dispensed with and in that the proportion of methacrylic anhydride is
reduced to one-half (to 0.5% of the acrylic monomers). The characteristics
of the product obtained are reported in Table II below.
Example 11
The procedure of Example 8 is repeated except that the proportion of
thioglycolic acid is doubled (to 0.1% of the acrylic monomers) and in that
the 2-ethylhexyl acrylate is replaced with an equivalent amount of butyl
acrylate. The characteristics of the product obtained are reported in
Table II below.
Example 12 (Comparative)
The procedure of Example 1 is repeated, except that the methacrylic
anhydride is totally omitted. The characteristics of the product obtained
are reported in Table II below.
Example 13
The procedure of Example 1 is repeated, except that the proportion of
methacrylic anhydride is doubled (to 2% of the acrylic monomers) and the
acrylic acid and methacrylic acid are totally omitted. The characteristics
of the product obtained are reported in Table II below.
TABLE II
Example Example Example Example Example Example
Example
Property 7 8 9 10 11 12
13
Adhesion 10.0 10.0 12.0 7.0 12.0 14.5
10.0
at 20 min
(23.degree. C.)
Adhesion at 24 h 18.0 16.0 16.0 11.0 18.0 15.0
13.0
(23.degree. C.)
Adhesion at 12.0 12.0 16.0 10.0 16.0 10.5
11.0
20 min after
7 days at 60.degree. C.
Shear >10,000 >10,000 >10,000 5000 >10,000 700 >10,000
Aggressiveness 12.0 11.0 12.0 9.0 10.0 13.5
11.0
pH 4.3 4.9 4.5 4.0 4.2 4.9
4.0
DMP.sup.(2) 310 350 313 320 440 310
350
.sup.(2) average particle size of the dispersion, expressed in nm.
The results collated in Table II show, when compared with Comparative
Examples 2 and 12:
a considerable improvement in the peel strength under severe conditions (7
days at 60.degree. C.), even when the proportion of methacrylic anhydride
is lowered to 0.5% by weight,
a substantial improvement in the shear strength, at the cost, in the latter
case, of a slight decrease in the peel strength at room temperature.
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